1. Field of the Invention
Aspects of the present invention relate to a cylinder type lithium ion secondary battery, and more particularly, to a cylinder type lithium ion secondary battery in which a center pin separating prevention part is formed in a hollow of an upper insulating plate to be preferentially bent toward an electrode assembly to enable insertion of the center pin after injection of electrolyte and to improve impregnation of the electrolyte.
2. Description of the Related Art
Recently, compact and light electrical and electronic apparatuses, such as mobile telephones, notebook computers, and camcorders, have been actively developed and produced. Battery packs are often built in with the portable electrical and electronic apparatuses so that the portable electrical and electronic apparatuses can operate at a location where an additional power source is not provided or available. The built in battery pack includes at least one battery to output a voltage of a uniform level to drive the portable electrical and electronic apparatus for a predetermined period.
An economical type of the battery back that came into use recently is a secondary battery that can be charged and discharged. Types of the secondary batteries include an Ni—Cd battery (a nickel-cadmium battery), an Ni—H battery (a nickel hydrogen battery), an Ni—MH battery (a nickel metal hydride battery) and a lithium ion secondary battery, such as a lithium battery and a lithium ion battery.
In particular, the operation voltage of the lithium ion secondary battery is commonly 3.6V, which is three times higher than the operation voltages of the Ni—Cd battery and the Ni—MH battery that are widely used today as power sources of the portable electronic apparatuses. As the energy density per unit weigh of the lithium ion secondary battery is also high, the use of the lithium ion secondary battery is rapidly increasing.
In the lithium ion secondary battery, lithium based oxides are used as positive electrode active materials and carbon materials are used as negative electrode active materials. In general, the lithium ion secondary battery is divided into a liquid electrolyte battery and a polymer electrolyte battery according to an electrolyte that is used. The lithium ion secondary battery in which the liquid electrolyte is used is referred to as a lithium ion battery and the lithium ion secondary battery in which the polymer electrolyte is used is referred to as a lithium polymer battery. The lithium ion secondary battery is manufactured to have various shapes and is appropriately referred to as a cylinder type, a polygon type, or a pouch type.
In general, the cylinder type lithium ion secondary battery includes an electrode assembly obtained by winding various components into a cylinder. The elements include a positive electrode plate coated with positive active materials, a negative electrode plate coated with negative active materials, and a separator positioned between the positive electrode plate and the negative electrode plate to prevent the positive electrode plate and the negative electrode plate from being shorted and to move only lithium ions, a cylinder shaped case to accommodate the electrode assembly and an electrolyte, and a cap assembly to seal the cylinder shaped case.
The cylinder type lithium ion secondary battery is manufactured by the following method. First, the positive electrode plate coated with the positive active materials is connected to a positive electrode tab and the negative electrode plate coated with the negative active materials is connected to a negative electrode tab. Then the coated positive electrode plate, the coated negative electrode plate, and the separator are laminated with each other. Thereafter, the laminated positive electrode plate, the negative electrode plate, and the separator are cylindrically wound to manufacture an electrode assembly. Then, the cylindrically wound electrode assembly is accommodated in the cylinder type (or shaped) case so that the electrode assembly is held within the case, the electrolyte is injected into the cylinder type case, and, the cylinder type case is sealed up by a cap assembly to complete the manufacture of the cylinder type lithium ion secondary battery.
Before inserting the electrode assembly into the cylinder type case, a lower insulating plate is inserted in order for the lower insulating plate to insulate the electrode assembly and the cylinder type case from each other. After inserting the electrode assembly into the cylinder type case and before sealing up the cylinder type case, an upper insulating plate is inserted in order for the upper insulating plate to insulate the electrode assembly and the cap assembly from each other. Meanwhile, a center pin is inserted into the central area of the wound electrode assembly to prevent the electrode assembly from becoming dislodged from the cylinder type case and to be used as a discharging path when gas is generated in the battery. Generally, after the insertion of the center pin into the central area of the electrode assembly, the electrolyte is injected. By inserting the center pin, the electrode assembly is more closely pressed against the case by the center pin and the various layers of the electrode assembly itself are pressed. Since the impregnation rate of the electrolyte is reduced with the center pin already inserted, it is advantageous to insert the center pin after the injection of the electrolyte in order to increase the impregnation of the electrolyte in the electrode assembly.
In the case of the polygon type lithium ion secondary battery, additional elements are further included. These include an insulating case to support the cap assembly and to insulate a terminal plate and the electrode assembly from each other.
However, the related art upper insulating plate is configured such that a diameter of a hollow formed in the upper insulating plate is smaller than the outer diameter of the center pin. The configuration prevents the center pin from separating from the electrode assembly when a shock, a jolt, or a blow is applied such as when the battery is dropped. Accordingly, it is impossible to insert the center pin after injecting the electrolyte. Moreover, although the diameter of the hollow formed in the upper insulating plate can be enlarged to be greater than that of the outer diameter of the center pin to enable the center pin to be inserted after the electrolyte is injected, the center pin then may be dislodged upward and become separated from the upper insulating plate to strike the lower side of a safety vent of a cap when an external shock or a blow is applied to the lithium ion secondary battery.